1. Technical Field
The present invention relates to a method of manufacturing a material for a rotary machine component, a method of manufacturing a rotary machine component, a material for a rotary machine component, a rotary machine component, and a centrifugal compressor.
Priority is claimed on Japanese Patent Application No. 2010-111204, filed on May 13, 2010, the content of which is incorporated herein by reference.
2. Background Art
Hitherto, a rotary machine such as a centrifugal compressor is used for supplying gas to a turbine in a gas turbine, a process of injecting gas into the ground during extraction of crude oil from an oil field, and the like. Since a high load is exerted on the components used in such a rotary machine, a high-strength metal material is used as the material of a rotary machine component such as an impeller.
On the other hand, in a centrifugal compressor used in an oil well environment or the like, a large amount of components that accelerate corrosion of the metal material, for example, hydrogen sulfide (H2S), carbon dioxide (CO2), and chlorine (Cl) is contained in a process gas which is a supply fluid, and the impeller comes into contact with a corrosive aqueous solution in which such gases are dissolved. Therefore, in the impeller on which a high load is exerted during driving of the centrifugal compressor, corrosion occurs due to the corrosive components described above, and furthermore, there is a possibility of stress corrosion cracking occurring and resulting in fracture.
As a material that endures the oil well environment as described above, for example, there are an austenitic stainless steel and a Ni-base alloy, and such metal materials are used in an oil well pipe and the like. However, such materials have low strength and thus there is a problem in that the materials may not be applied to components used in a rotary machine such as an impeller of a centrifugal compressor.
Therefore, hitherto, as the material for the impeller of the centrifugal compressor, for example, a precipitation-hardening martensitic stainless steel such as 17-4 PH and a martensitic stainless steel such as SUSF6NM are applied. However, such materials never have high corrosion resistance, and as above, there is a possibility of corrosion or stress corrosion cracking occurring due to the corrosive components.
In addition, employing a material similar to SUS329J4L having corrosion resistance and the like as the metal material used in the impeller is proposed (for example, refer to Non Patent Document 1). However, even though such a material as described in Non Patent Document 1 is used, in a case where the proportion of corrosive components contained in a fluid increases, there is a possibility of corrosion or stress corrosion cracking occurring as above.
In addition, employing a precipitation-hardening Ni-base alloy such as Inconel 718 which has both corrosion resistance and strength as the material of the impeller is considered. However, the precipitation-hardening Ni-base alloy as described above is expensive, and thus there is a problem in that manufacturing cost is increased.
Here, a duplex stainless steel is known as a metal material which has sufficient corrosion resistance and strength and is relatively cheap in practice (for example, refer to Patent Documents 1 to 3). Therefore, in recent years, the duplex stainless steel has been appropriately used as materials for rotary machine components such as the impeller of the centrifugal compressor.
However, in a case where the duplex stainless steel as described above is used for a rotary machine component such as the impeller, there are problems which may be described as follows.
First, in a case where the duplex stainless steel is subjected to isothermal holding at about 450 to 1000° C., or to slow cooling at about 450 to 1000° C. in a welding process during manufacturing of components, various heat treatment processes, and the like, 475° C.-embrittlement or σ-embrittlement occurs. Therefore, the toughness of the material is degraded, and there is a problem in that cracking is likely to occur in a manufacturing process of a corresponding component or during driving of a rotary machine such as the centrifugal compressor.
In addition, it is known that in an annealing process which is performed after performing a welding process or a machining process during manufacturing of component after performing a solution treatment on a material made of the duplex stainless steel, in order to effectively remove residual stress, generally, it is appropriate to perform heating at as high a temperature as possible.
However, in a case where the duplex stainless steel material is held at a high temperature, 475° C.-embrittlement or σ-embrittlement occurs. Therefore, as above, there is a problem in that cracking is likely to occur during the manufacturing process of a corresponding component or during driving of a rotary machine (see the graph of FIG. 9). Therefore, hitherto, in the annealing process performed after the welding process or the machining process, a heat treatment is performed at a temperature of 300 to 400° C. which is insufficient to remove residual stress within a typical heat treatment time.